piston won't slide into cylinder...??

So i have the peugeot 103 that I am working on, and the piston will not slide back into the cylinder. Here is the weird part, this engine ran two days ago.

I just pulled the top end last night to clean up the carbon build up on the piston crown as well as the head. I didnt touch the sides of the piston with anything other than my fingers, i didnt touch the inside of the cylinder at all.

The piston won't even slide into the cylinder w/o rings. It feels like the piston swelled about .002 of an inch.totally bizarre.

Anyway, is this kind of thing normal for peugeots? Do they have VERY small clearance tolerances? I could force the thing in there if i wanted to, but then it would just be seized, and that would in turn fuck my top end.

Ideas?

Re: piston won't slide into cylinder...??

maybe the cylinder contracted from the cold? weird. i was about to say compress your rings. did you use 2 stroke oil to lube it in?

Re: piston won't slide into cylinder...??

yep. this thing is lubed up and ready to go. it is quite bizarre.

that's what i get for fixing what isn't broken.

Re: piston won't slide into cylinder...??

did you line up the ring openings with the little nubbin in the piston groove? I didnt the first time and that is why i didnt get mine on. They are both on the front of the piston facing the exhaust port on two differant sides.

Re: piston won't slide into cylinder...??

yep. even tried to fit the pison w/o rings at all(just so see if it would fit, not to run it this way) and it wont fit this way either.

Re: piston won't slide into cylinder...??

Leon Swarmer /

Have you checked to make sure you have the piston right on the connecting rod? or if you did't take it off are you sure you have your cylinder with the exhaust port facing the right way?

Re: piston won't slide into cylinder...??

Jason Luther /

okay, here is what i see happening. you first tried to put the cylinder over the piston, but got hung up on the rings. then when you removed the piston from the motor, and then the rings from the piston, you tried to put it through the _top_ of the cylinder, which then wouldnt fit because of the 'wear ring' around the top. did i nail it?

Re: piston won't slide into cylinder...??

no. first i tried to reassemble the top end on the bike...no go. then i took the piston off the crank and tried to slide the piston into the bottom of the cylinder(the way it would be if it were on the bike)....no go, then i took the rings off and tried....no go.

like i said, its almost like the piston swelled up, or the cyl. contracted. this is however not possible, b/c they were both in the same place on my shelf in the basement(heated basement) at room temperature.

shit be crazy.

Re: piston won't slide into cylinder...??

thats crazy. try heating the cylinder and cooling the piston

Re: piston won't slide into cylinder...??

yah, i could do that, but if it slides in fine, wont it just seize up when the temp in both equalizes?

Re: piston won't slide into cylinder...??

Jason Luther /

something is not right here. do you have other pistons lying around that may have gotten mixed up?

Re: piston won't slide into cylinder...??

I was going to ask if you were trying to install it from the bottom or the top, but you already answered that. Is it possible that you could have switched pistons accidentally?

Re: piston won't slide into cylinder...??

Not really. I mean, I do have a bunch of pistons laying around, but they are all for 125cc and up bikes, so they are a bit bigger than a moped piston.

But good call on that, as this was my first thought as well.

Re: piston won't slide into cylinder...??

man that is weird. if you don't have annother piston or cylinder that you switched it with, I have a hone that should work.

Re: piston won't slide into cylinder...??

That is the first thing im trying tomorrow. Im going to take it to one of the many scooter shops around and have them hone it until it works. one time through should probably do it.

Re: piston won't slide into cylinder...??

Jason Luther /

was it sitting on the shelf for long? is it a cast iron sleave cylinder? is it perhaps rusted?

Re: piston won't slide into cylinder...??

it was sitting on the work bench for exactly 12 hours. im going to run a hone through it in the morning and see what happens.

Re: piston won't slide into cylinder...??

I've heard that hones scuff up the chrome surface, and that you should only use them on cast iron cylinders.

Re: piston won't slide into cylinder...??

really? hmm...that sort of throws a wrench in my plan.

Re: piston won't slide into cylinder...??

Don't try to hone a chrome bore. I've heard you can lightly, lightly hone a Nikasil bore, but even that seems dodgy. Messing up a chrome bore is expensive to replate. Have you measured your piston and bore yet? This is a really wierd problem. You didn't drop the cylinder and bend one of the ears or something, did you?

Re: piston won't slide into cylinder...??

i know its a super weird problem, i didnt drop any of it. took it off the bike, it sat on the work bench from yesterday until today and now it wont go in...i am completely stumped. the ONLY thing i can think of, is that the first time i put the wrist pin in, i bent something. thats all it could be. i guess ill find another piston and try that.

Re: piston won't slide into cylinder...??

put the piston in the fridge for a couple hours and put the cylinder on a heating pad or something then assemble quickly with 2 stroke oil.Jim

Re: piston won't slide into cylinder...??

Then when everything hits room temp, it will lock up.

Re: piston won't slide into cylinder...??

exactly.

Re: piston won't slide into cylinder...??

damn thats weird. are yopu sure you kept them in the same environments? even so metal shouldnt expand THAT much. they are made out of different materials arent theyt? the cy5linder caasing shoulkd be aluminum and the piston sleeve could be steel and chromed. that might not expand as much as the material of the piston.

Re: piston won't slide into cylinder...??

they were sitting next to eachother on my work bench in be heated basement. there is no way they heat/cold expanded/shrunk enough to make this not work.

now im starting to think that the cylinder may have been a little warped when the guy who had it before me set it up, and now that i have released the constant pressure it wont work...either way, shit be crazy.

Re: piston won't slide into cylinder...??

I've heard that pistons can become oval shaped over time. Could this be the problem? I assume you've tried twisting it in?

Re: piston won't slide into cylinder...??

i hear you there dont fix it if it ant broken. i've learned my lesaon once or twice in my day

Re: piston won't slide into cylinder...??

"In my day" lol

Re: piston won't slide into cylinder...??

Negative. if that's the same piston that was in there and wasn't frozen and if the new rings are the right ones it will be fine!the problem is either both of those items are at different temps probably because they are made of different alloys and you don't know it one holds heat better than the other but once they are together they will lose heat the samethrough convection.why did you take it apart.jim

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